Migration and evolution of dissolved organic matter in landfill leachate-contaminated groundwater plume

Abstract

Groundwater pollution around landfill sites is becoming a global environmental problem. The hydrochemistry of dissolved organic matter (DOM) in landfill leachate-contaminated groundwater plume has been investigated extensively. The spatial migration and evolution of DOM, the relationship between hydrochemistry and DOM dynamics, and the role of microorganisms in DOM transformation are still largely unclear. In this study, UV–vis, 3D-EEM PARAFAC and principal components analyses were combined to investigate the migration and evolution of DOM. The results show that when the contamination plume gradually diffuses, the molecular weight of DOM in downstream groundwater tends to be high, while the humification degree is low and DOM is mostly derived from microbial metabolism. Compared with humic-like and fulvic-like substances, protein-like substances have a higher migration capability, making them suitable indicators of groundwater pollution. Under low-permeability aquifer medium (K < 10−7 cm/s), the DOM pollution was easy to rebound. An evident positive correlation exists between electrical conductivity and the maximum fluorescence intensity of humic-like and fulvic-like substances. Venn diagram shows that 15.31% (117 of 764) of the species were unique in the upstream and could not be detected in downstream groundwater. In comparison, 43.05% (489 of 1136) of the species were unique in the downstream and 382 were not detected in upstream groundwater. The main microorganisms (such as Polynucleobacter, Comamonadaceae, Desulfobulbus, and Magnetovibrio) play a pivotal role in DOM transformation in the aquifer. This study provides a novel insight into the monitoring, early warning and remediation of groundwater pollution in landfills.